Membrane method of making drilling fluids containing microbubbles
Drilling fluid is reduced in density while under pressure and prior to injection in the well by creating microbubbles of gas formed on transportation through a membrane while maintaining a transmembrane pressure difference sufficient to create the microbubbles.
1 . Method of reducing the weight of a liquid well drilling fluid comprising (a) maintaining said drilling fluid at a pressure of at least 100 psi, and (b) passing a gas through a microporous medium into said well drilling fluid in the form of microbubbles, thereby reducing the weight of said well drilling fluid.
2 . Method of claim 1 including flowing said well drilling fluid through a microporous membrane tube comprising said microporous medium.
3 . Method of claim 2 whereby the weight of said well drilling fluid is reduced at least 20%.
4 . Method of claim 2 wherein the weight of said drilling fluid is reduced to a weight in the range of four to eight pounds per gallon.
5 . Method of claim 1 wherein the microbubbles have diameters from 100 nanometers to 100 micrometers
6 . Method of claim 1 wherein said microporous membrane is fixed in a microporous membrane tube having pores of 0.1 to 50 microns and said drilling fluid flows through said microporous membrane tube in a cross flow mode.
7 . Method of claim 1 wherein said gas is air.
8 . Method of claim 1 wherein said gas is at least 90% nitrogen.
9 . Method of claim 1 wherein said liquid well drilling fluid contains at least one of (c) a surfactant in an amount effective to reduce the interfacial tension between the gas and the aqueous fluid (d) a viscosity-enhancing polymer in an amount effective to enhance the viscosity of said aqueous drilling fluid, and (e) a suspension stabilizer in an amount effective to stabilize the suspension of microbubbles in said aqueous drilling fluid.
10 . Method of claim 1 including maintaining a pressure difference across said microporous medium of between 50 and 150 psi
11 . Method of injecting a liquid drilling fluid having a reduced density into a wellbore at a pressure in excess of 250 psi comprising (a) contacting said drilling fluid at a fluid pressure of at least 250 psi with a microporous membrane and (b) introducing microbubbles of gas into said fluid to reduce the density of said fluid by permeating said gas through said microporous membrane, said gas being under a pressure greater than the pressure of said liquid drilling fluid, and (c) injecting said drilling fluid into said wellbore.
12 . Method of claim 11 wherein (d) said contacting of said drilling fluid with said microporous membrane comprises flowing said drilling fluid through at least one tube comprising said microporous membrane and wherein (e) said permeating of said gas through said microporous membrane comprises contacting the exterior of said at least one tube with said gas at a pressure in excess of 250 psi.
13 . Method of claim 12 wherein said at least one tube has a tortuous flow pattern.
14 . Method of claim 11 wherein (d) said contacting of said drilling fluid with said microporous membrane comprises flowing said drilling fluid in contact with the outside of at least one tube comprising said microporous membrane and wherein (e) said permeating of said gas through said microporous membrane comprises contacting the inside of said at least one tube with said gas at a pressure in excess of 250 psi.
15 . Method of drilling a well comprising (a) imposing a pressure suitable for drilling a well on a drilling fluid, said pressure being at least 100 psi, (b) creating microbubbles of gas in a said drilling fluid while under pressure by passing gas into said fluid through a microporous membrane, thereby reducing the density of said fluid by at least 20 percent; (c) circulating said fluid containing said gas to said well to remove drill cuttings therefrom, (d) recovering said fluid from said well, and (e) removing said drill cuttings from at least a portion of said fluid to make a recycle fluid.
16 . Method of claim 15 wherein said creating microbubbles in step (b) comprises maintaining a transmembrane pressure difference between 50 and 150 psi.
17 . Method of claim 15 including (f) creating microbubbles of gas in at least a portion of said recycle fluid by passing gas into it through a microporous membrane, and (g) using said at least a portion of said recycle fluid containing said gas as a drilling fluid.
18 . Method of claim 17 wherein said pressure in step (a) is at least 1000 psi.
19 . Method of claim 15 wherein said microbubbles have diameters from 100 nanometers to 100 micrometers.
20 . Method of claim 15 wherein said drilling fluid contains at least one of (i) a surfactant in an amount effective to reduce the interfacial tension between the gas and the aqueous fluid (ii) a viscosity-enhancing polymer in an amount effective to enhance the viscosity of said aqueous drilling fluid, and (iii) a suspension stabilizer in an amount effective to stabilize the suspension of microbubbles in said aqueous drilling fluid.